Enderman Problems

The amount of Endermen that spawn in a Enderman farm is little, and isn't good enough for farms. Plus some Enderman do not walk off the trapdoors (image below) they stand there until they either teleport back onto safe platform (farm) or they fall ONLY when another Enderman pushes them down. The Enderman don't seem to immediately NOTICE the Endermite like they do in Java as well.